The mcu AT89L4052 has 256 bytes internal RAM

the lower 128 bytes may be accessed by direct or indirect method
and the upper 128 bytes of RAM may be accessed by indirect method.
The upper 128 bytes when accesed by direct method access the SFRs.



So, you may setup the SP to an upper point than #7FH, so there is enough room
between #80H and point to accesed by indirect method using the instructions

Arithmetic
 ADD A, @Ri
 ADDC A, @Ri
 SUBB A, @Ri
 INC @Ri
 DEC @Ri

Logical
 ANL A, @Ri
 ORL A, @Ri
 XRL A, @Ri

Data Transfer
 MOV A, @Ri
 MOV direct, @Ri
 MOV @Ri, A
 MOV @Ri, direct
 MOV @Ri, #data
 XCH A, @Ri
 XCHD A, @Ri

Branching
 CJNE @Ri, #data, rel

 

you have to load an index register Ri like R0, or R1 with the desired address and using
the above instructions you can access any byte or bit of the internal RAM.

Of course care should be given to leave enough space for Stack Pointer
eg. set SP to #9F to have room from #0A0h to #0FFh there or 96bytes for stack usage.
and by that setting there are from #80h to #9Fh = 32d bytes to use by the indirect method.

You may use this reference
http://www.atmel.com/dyn/resources/prod_documents/doc3547.pdf

K.L.Angelis